1. Field of the Invention
This invention concerns an apparatus for counterbalancing tongs in an oil derrick as well as assisting in lowering and raising the tongs to position them around a workpiece.
2. General Discussion of the Background
The general background of the present invention is discussed in greater detail in my prior copending application Ser. No. 379,276 filed May 17, 1982 which has been incorporated by reference.
In the oil exploration and production industry, it is common to use a pair of tongs to assemble such things as drill strings. The drill strings are provided with internally and externally threaded ends which mate in threaded engagement with adjacent segments to assemble successive segments of pipe. The successive segments must be rotated in order to engage the threads on successive segments.
Rotation of the segments of pipe is performed by a tong which is a jaw-like member defining a semicircular recess in which a plurality of high coefficient of friction rolling members are located. The tong is positioned adjacent the pipe, the roller is placed in frictional engagement with it, and the rollers are then hydraulically actuated in a manner known in the art to rotate the section of pipe. A pair of such tongs are often used in assembling successive sections of the pipe. The second tong, however, only performs a supporting function without necessarily actively rotating the pipe.
In order to use tongs, it is necessary to hold them in position next to the workpiece being rotated so that the rollers of the tong can engage the work piece and rotate it. In the prior art, these tongs have been suspended by a cable which is attached at one end to the tong and at its second end to a counterweight, the cable being journalled over an elevated pulley. A counterweight is usually of an appropriate weight that will suspend the tong at a desired height while permitting a worker to make adjustments in the height of the tong without exerting himself too greatly. There are serious drawbacks to the tong counterbalances, however, because these counterbalances do not permit fine movement adjustments of the tongs in relation to the workpiece. Another drawback is that the counterbalanced tongs are subject to destabilizing forces that can quickly and dangerously raise or lower the tong, thereby injuring any workmen in the vicinity.
It is accordingly an object of this invention to provide an apparatus for counterbalancing tongs and assisting in lowering and raising the tongs within an oil derrick.
It is another object of the invention to provide such an apparatus that will permit fine movement adjustments of the height of the tongs.
Yet another object of the invention is to provide such an apparatus in which the height of the tongs is under positive control by workmen at all times.